The term Crude Tall Oil, in the following CTO, refers to a by-product stream obtained during pulping of wood in the Kraft pulping process. The name tall oil (TO) originated as anglicisation of Swedish “tallolja” (“pine oil”). The TO comprises of fraction having acidic properties (—COOH functional group) typically about 75-80 wt. % and neutral fraction up to 25 wt. %. The latter fraction is often referred to as unsaponifiable fraction. The unsaponifiable fraction comprises of wide spectrum of components such as hydrocarbons, fatty alcohols, phytosterol-type alcohols, aldehydes, etc. as well as high molecular weight components originating from internal reactions between constituents of acidic and neutral fractions. The fraction comprised of components with acidic functionality on the other hand, can be further subdivided into two large fractions namely, (i) fatty acids fraction and (ii) resin acids fraction each containing a number of individual components. From this description of the tall oil composition it is obvious that the CTO represents an attractive pool of renewable fine chemicals, which are nowadays gaining much attention in view of stringent environmental regulations and rising prices of fossil oils.
At present, CTO fractionation is done typically by vacuum distillation. The objectives are rather straight forward, to split the CTO into two fractions (i) acidic fraction up to 75 wt. % and fraction of less importance called (ii) tall oil pitch (TOP). The acidic fraction is further processed in a sequence of fractionation towers operating at high temperatures and relatively high vacuum to obtain streams enriched in fatty acids and resin acids. TOP is typically returned to the pulp mills as internal fuel or used as biofuel in heat and power plants. It is important to minimize the fraction of TOP produced in CTO refining processes and the present invention is directed to a CTO refining process with high yield of valuable chemicals and biofuels for automotive use.
A process for refining CTO into valuable biofuels is disclosed in WO 2009/131510. In WO 2009/131510 there is disclosed a method for conversion of crude tall oil into high-quality diesel fuels comprising the steps of (a) removal of non-oil contaminants present in the crude tall oil and recovering valuable organic compounds present in the crude tall oil, thereby forming a refined tall oil stream; (b) removal of the volatile fraction of the refined tall oil stream from step a), thereby forming a volatiles free oil stream comprising organic components with boiling points, at atmospheric pressure, of 170° C. or higher; (c) separation in a vacuum fractionation tower of the volatiles free oil stream of step b) into two process streams or phases wherein a first process stream or phase is substantially comprising components with boiling points, at atmospheric pressure, in the range of 170-400° C. and a second process stream or phase is substantially comprising components with boiling points, at atmospheric pressure, over 400° C.; and (d) lowering the oxygen content in the stream comprised of components with boiling points in the range 170-400° C. from step c) by decarboxylation and/or decarbonylation.
One aim of the present invention is to provide an improved way of refining CTO. Another specific goal according to the present invention is to provide an improved pre-treatment process of CTO. Yet another specific target of the present invention is to provide an improved process for the production of resin acids and refined tall diesel (RTD in the following) from CTO. There are also other aims of the present invention which are presented below.